1. Field of the Invention
The present invention relates to nanoporous metal oxide materials effective as catalyst supports for hydrogen production reaction and so on, catalyst supports, and catalysts for hydrogen production reaction using such catalyst supports.
2. Related Background Art
Various catalysts have been developed so far for hydrogen production reaction to generate hydrogen as a fuel in fuel reforming systems such as fuel cells. Various kinds of substrates including honeycomb filters on which a metal oxide such as alumina, and a noble metal such as platinum, rhodium and palladium are supported, have been generally used as such catalysts.
In general, powder obtained by wet grinding method has been heretofore used as such metal oxides. For example, Japanese Patent Application Laid-Open Gazettes No. Hei. 10-182155 (Document 1) and No. 2002-79097 (Document 2) disclose methods to obtain compound metal oxide powder by preparing oxide precursors from salt solutions of aluminum, cerium and zirconium by coprecipitation method and then calcining the yielded oxide precursors in the air. In addition, in Japanese Patent Application Laid-Open Gazette No. Hei. 7-300315 (Document 3), a method is disclosed to obtain compound metal oxide powder by first adding boehmite alumina powder to a mixed solution of salt solutions of cerium and zirconium, and the mixture was then stirred followed by the drying and calcination of the resultant.
However, when conventional metal oxide powder like that described in Documents 1 to 3 is used, adhesion to substrates (especially to metal substrates) is not always sufficient and there is also a limitation for formation of thin film coating formed on the substrate. Therefore, it has been a problem because of difficulties in supporting such conventional metal oxide powder when using substrates such as metallic honeycomb filters and high density (high integration) honeycombs (e.g. microchannels equal to or greater than 1200 cell/inch2) with narrower tubular passages than those of common honeycomb filters, as well as limitation in the improvements of reforming performances.